1. Field of the Invention
The present invention relates to an evacuation method and a vacuum processing apparatus.
2. Description of the Related Art
In vacuum processing apparatuses, a CD (Critical Dimension) control is performed to control a shift amount of a post-etching pattern dimension relative to a pre-etching mask dimension. However, in an etching process after maintenance for cleaning a vacuum chamber, a CD shift occurs in which a CD value deviates from a setting value. To solve this, it is proposed to perform the etching process after stabilizing an atmosphere in the vacuum chamber by seasoning the inside of the vacuum chamber after the cleaning, thereby preventing the CD shift from being generated. However, when performing the seasoning, a start of the etching process after the maintenance is delayed. Therefore, stable operation inside the vacuum chamber after the maintenance and reduction of a period of time until starting the etching process after the maintenance are desired.
In response to this, to reduce a period of time required to evacuate the vacuum chamber, a variety of evacuation methods are proposed. For example, Japanese Laid-Open Patent Application Publication No. 2002-249876 proposes a method of setting the inside of a chamber at a positive pressure state that is equal to or higher than the atmospheric pressure once by introducing an inactive gas into the chamber after starting an evacuation, and then further continuing the evacuation.
However, in the evacuation method of Japanese Laid-Open Patent Application Publication No. 2002-249876, when the pressure inside the vacuum chamber is reduced, moisture having attached to wall surfaces and surfaces of component parts that are exposed to the atmosphere during the maintenance, starts evaporating. After that, when the pressure inside the vacuum chamber continues to be reduced, the temperature of moisture decreases by adiabatic expansion eventually to a temperature lower than zero degrees C., and sometimes to a temperature between about −15 degrees C. to about −30 degrees C. At this time, moisture inside the vacuum chamber not having evaporated may freeze.
Frozen moisture continues to evaporate for a long time and traps moisture not yet frozen in small recesses in the wall surfaces and the like, thereby making it difficult to reduce a period of time of the evacuation. Moreover, the frozen moisture may cause a failure such as generation of particles, abnormal discharge, and corrosion of component parts.